The present invention relates to an electronic apparatus, to an electronically-controlled timepiece having the same, and to a power supply control method.
Concerning an electronically-controlled mechanical timepiece for displaying accurate time, there is a known timepiece described in Japanese Unexamined Patent Application Publication No. 8-5758. In this timepiece, mechanical energy when releasing a spring is converted into electrical energy by a power generator. A rotation control unit is activated by the electrical energy, and a current value flowing through a coil of the power generator is controlled. Hence, hands fixed to a wheel train are accurately driven, thus displaying accurate time.
In this timepiece, the electrical energy from the power generator, that is, the power supply for supplying electrical energy, is supplied to a capacitor once, and power from the capacitor is employed to drive the rotation control unit. Since AC electromotive force in synchronism with a rotation period of the power generator is input to the capacitor, it is not necessary to store power for enabling the rotation control unit provided with an IC (an electronic circuit and a logic circuit) and an oscillation circuit (quartz crystal oscillator) to operate for a long period of time. Hence, a capacitor with a relatively small capacitance, such as a 10 xcexcF capacitor, capable of operating the IC and the oscillation circuit for a few seconds is employed.
This electronically-controlled mechanical timepiece does not require a motor since it uses the spring as a power source for driving the hands. Therefore, the characteristics of the timepiece are that it requires a few components and is inexpensive. In addition, it is only necessary to generate small electrical energy for driving the electronic circuit. The timepiece can be operated by small input energy.
However, this conventional electronically-controlled mechanical timepiece has drawbacks as follows. Specifically, when performing time adjustment (hands adjustment) which is generally performed by pulling out a crown, hands for hour, minute, and second are stopped so that the time can be accurately adjusted. Since stopping the hands would mean stopping the wheel train, the power generator is also stopped.
Therefore, the input of electromotive force from the power generator to the capacitor is stopped. In contrast, the IC and the oscillation circuit are continuously driven. Electrical charges accumulated in the capacitor are discharged to the IC side, thus reducing a terminal voltage. As a result, the rotation control unit, that is, the oscillation circuit or the like, is also stopped.
When the IC stops oscillating, power consumption is reduced, thus significantly slowing down voltage reduction in the capacitor. When a user has trouble in adjusting the time, and a voltage of the capacitor is reduced below an oscillation stopping voltage, the capacitor is often at a voltage of approximately 0.3 to 0.4 V which is slightly smaller than the oscillation stopping voltage. When the time adjustment (hands adjustment) is performed for a very long period of time, such as for more than several tens of minutes, the capacitor may completely discharge, and the voltage may be reduced to xe2x80x9c0xe2x80x9d.
When the hands adjustment is completed and the crown is pushed in, thus starting rotation of the power generator, some time is required to boost the voltage of the capacitor by a charging current of the power generator and to cause the oscillation circuit and the IC to start operating. In particular, when a generated current is small, power is consumed by a leakage in the IC, and the voltage of the capacitor is not increased. Hence, the system is not promptly started. This results in taking time to start brake control and to perform time control. Although the time adjustment (hands adjustment) is performed, there is an error in the designated time.
Besides the electronically-controlled mechanical timepiece, a self-winding generating-type timepiece for moving an oscillating weight and generating power, and an electrically-controlled timepiece, such as a solar rechargeable-type timepiece, provided with various generators (power supplies) have a similar problem. When a power generator is stopped upon hands adjustment, and when a capacitor is discharged, some time is required to activate electronic circuits due to a leakage in the IC or the like, even when the power generator is activated.
Besides the electrbnically-controlled timepiece, there are various electronic apparatuses provided with a power generator (power supply), a capacitor, and electronic circuits such as an IC and an oscillation circuit. In addition, there are various electrical apparatuses provided with, instead of a power generator, a power supply such as a commercial power supply or a car battery. Concerning these electrical apparatuses, there is a problem in that, when the power supply starts operating, that is, when the power generator is started or when power is first supplied from the power supply, some time is required to activate the IC and the oscillation circuit, due to a leakage in the IC or the like.
It is an object of the present invention to provide an electronic apparatus, an electronically-controlled timepiece, and a power supply control method in which electronic circuits, such as an IC and an oscillation circuit, are rapidly activated when a power supply starts operating.
An electronic apparatus according to the present invention, including a power supply, a capacitor for accumulating power from the power supply, and an electronic circuit driven by the power from the capacitor, comprises a power supply control unit for not supplying the power from the capacitor to the electronic circuit until a voltage of the capacitor reaches a preset voltage, and for supplying the power from the capacitor to the electronic circuit when the voltage of the capacitor becomes equal to or greater than the preset voltage.
According to the present invention, the power supplied from the power supply, such as a power generator, is accumulated in the capacitor. Since the power supply control unit controls the power not to be supplied from the capacitor to the electronic circuit until the voltage of the capacitor reaches the preset value, a leakage current is not generated, which is part of the power supplied from the power supply flowing into the electronic circuit. Most of the supplied power (generated power or the like) can be supplied to the capacitor. Therefore, the time required to increase the voltage of the capacitor so as to reliably activate the electronic circuit, such as an IC, is reduced. The time until activation of the electronic circuit, such as the IC or an oscillation circuit, is reduced.
Due to characteristics of a quartz crystal oscillator, the quartz crystal oscillator oscillates more readily when a rapidly-changing voltage is suddenly applied, compared to when a gradually-increasing voltage is applied. In other words, the quartz crystal oscillator can oscillate even at a low voltage. By applying the voltage of the capacitor that has reached the preset voltage to the electronic circuit, a relatively large voltage can suddenly be applied to the electronic circuit. This reduces the oscillation starting time of a quartz crystal oscillating circuit of the electronic circuit.
The power supply may be a power generator. Preferably, when the power generator starts operating, the power supply control unit does not supply the power from the capacitor to the electronic circuit until the voltage of the capacitor reaches the preset voltage. Preferably, the power supply control unit supplies the power from the capacitor to the electronic circuit when the voltage of the capacitor becomes equal to or greater than the preset voltage.
Concerning the power supply, a commercial power supply or a car battery can be employed. Alternatively, various power generators can be employed, including a power generator for rotating a rotor and generating power by means of electromagnetic transduction, a piezoelectric generator for applying stress to a piezoelectric device and generating power, a solar battery, and a thermo-electric generator. These power generators may stop operating in accordance with operating conditions. When the present invention is applied to each of these power generators, the starting time to start up a system in which the power generator is activated is shortened. Hence, the present invention is advantageous.
Preferably, the power supply control unit includes a comparing circuit for comparing the voltage of the capacitor and the preset voltage, and an operation control unit for controlling activation and deactivation of the comparing circuit.
With this construction, the comparing circuit can be stopped by the operation control unit after the voltage of the capacitor reaches the preset voltage and the supply of power starts. The comparing circuit can be operated only when it is necessary to perform comparison of the voltage of the capacitor. Hence, it is possible to reduce power consumed by the power supply control unit, and energy conservation is performed for the electronic apparatus.
Preferably, the electronic circuit includes a constant voltage circuit driven by the voltage of the capacitor via the power supply control unit, an oscillation circuit driven by an output of the constant voltage circuit, and an oscillation detecting circuit for detecting whether the oscillation circuit is oscillating and for outputting an oscillation detection signal. The operation control unit may control activation and deactivation of the comparing circuit in response to the oscillation detection signal of the oscillation detecting circuit.
It is preferable that the operation control unit deactivate the comparing circuit when the oscillation circuit is oscillating, and activate the comparing circuit when the oscillation stops.
For example, when the power generator is activated by a spring, the generated voltage is gradually reduced as the spring is released. Activation and deactivation of the comparing circuit can be controlled in response to the oscillation detection signal of the oscillation detecting circuit. Hence, the comparing circuit is first activated when the oscillation of the oscillation circuit is stopped, and the comparing circuit is stopped when the oscillation circuit is in operation. Accordingly, the supply of power to the electronic circuit can be continued until the oscillation circuit is stopped, and the operating time of, the electronic circuit, such as the oscillation circuit or the IC, can be prolonged.
The operation control unit is not limited to one that activates/deactivates the comparing circuit in response to the output signal of the oscillation detecting circuit. For example, the operation control unit may activate/deactivate the comparing circuit in response to a signal from a timer or the like that outputs a predetermined signal at a constant interval.
When the power is not supplied from the capacitor to the electronic circuit, and when the voltage of the capacitor is increased to be a first preset voltage or greater, the power supply control unit may supply the power from the capacitor to the electronic circuit. When the power is supplied from the capacitor to the electronic circuit, and when the voltage of the capacitor is reduced below a second preset voltage which is set to be not greater than the first preset voltage, the power supply control unit may stop supplying the power from the capacitor to the electronic circuit.
In such cases, when the power is not supplied from the capacitor to the electronic circuit upon activation of the system or the like, and when the voltage of the capacitor becomes equal to or greater than the first preset voltage, the power is supplied to the electronic circuit. In contrast, when the power is supplied from the capacitor to the electronic circuit upon deactivation of the system or, the like, and when the voltage of the capacitor is reduced to the second preset voltage or less, the supply of power to the electronic circuit is stopped. By appropriately setting the second preset voltage, the time until the power is started to be supplied to the electronic circuit is prolonged, thus increasing the operating time of the electronic circuit, such as the oscillation circuit or the IC. Since the second preset voltage, that is, the value for stopping the system, can freely be set, the electronic circuit can be operated as long as the voltage for stably operating the IC or the like is ensured. By setting the deactivation voltage in accordance with characteristics of the electronic circuit, such as the IC, the electronic circuit can be operated in a stable manner.
The electronic circuit may include an oscillation circuit. The power supply control unit may supply the power from the capacitor to the electronic circuit when the voltage of the capacitor is increased to a first preset voltage or greater, and may stop supplying the power from the capacitor to the electronic circuit when the voltage is reduced and the oscillation circuit is thereby stopped.
In such cases, the power can be supplied to the electronic circuit until the oscillation circuit stops. When the oscillation circuit stops, the supply of power from the capacitor to the electronic circuit is stopped. Therefore, the power is not supplied wastefully, and, the voltage reduction in the capacitor is reduced. The capacitor can rapidly be boosted when the power is subsequently generated, and the oscillation circuit rapidly starts oscillating.
An electronically-controlled timepiece of the present invention includes an electronic apparatus as described hereinabove, and a time indicator in which speed is regulated by the electronic circuit of the electronic apparatus.
According to the electronically-controlled timepiece, the time until activation of the electronic apparatus is shortened, and the speed of the time indicator can rapidly be regulated. When the timepiece returns from performing hands adjustment, the timepiece can rapidly return to a normal control state. An error in the designated time upon returning from the hands adjustment is minimized.
Concerning the electronically-controlled timepiece, an electronically-controlled mechanical timepiece can be employed. In such a case, the power generator is driven by a mechanical energy source engaged therewith via mechanical energy transfer means. The time indicator is connected to the mechanical energy transfer means, and the electronic circuit controls the power generator, thus regulating the speed of the time indicator.
In the electronically-controlled mechanical timepiece, the capacitor has a low capacitance. When the power generator is stopped for three to five minutes or more in order to adjust the hands, the capacitor is discharged, and the electronic circuit is thereby stopped. When the present invention is applied to the electronically-controlled mechanical timepiece, the capacitor can rapidly be charged even when the capacitor is discharged by adjusting the hands. An error in the designated time upon returning from the hands adjustment is minimized.
A power supply control method of the present invention is performed for an electronic apparatus including a power supply, a capacitor for accumulating power from the power supply, and an electronic circuit driven by the power from the power supply. According to the power supply control method, the power is not supplied from the capacitor to the electronic circuit until a voltage of the capacitor reaches a preset voltage. The power is supplied from the capacitor to the electronic circuit when the voltage of the capacitor becomes equal to or greater than the preset voltage.
Preferably, the power supply is a power generator. When the power generator starts operating, the power may not be supplied from the capacitor to the electronic circuit until the voltage of the capacitor reaches the preset voltage. When the voltage of the capacitor becomes equal to or greater than the preset voltage, the power may be supplied from the capacitor to the electronic circuit.
According to the present invention, most of the power (for example, power generated by the power generator upon activation) supplied from the power supply can be supplied to the capacitor. The time until the voltage of the capacitor is boosted so as to reliably operate the electronic circuit, such as the IC, is shortened. Hence, the time until activation of the electronic circuit, such as the IC or the oscillation circuit, is shortened.
When the voltage of the capacitor is reduced below a second preset voltage, it is preferable to stop the supply of the power from the capacitor to the electronic circuit.
The electronic circuit may include an oscillation circuit. When the voltage of the capacitor is reduced and the oscillation circuit is thereby stopped, the supply of the power from the capacitor to the electronic circuit may be stopped
By adopting this supply method, it is possible to prolong the time until the power is started to be supplied to the electronic circuit. Hence, the operating time of the electronic circuit, such as-the oscillation circuit or the IC, is increased.